Resonance and amplifying chamber for banjos



NOV. 30 1926.

- F. J. BACON ET AL RESONANCE AND AMPLIFYING CHAMBER FOR BANJOS FiledApril 18, 1924 5 Sheets-Sheet 1 zlwmmtow 4 1 J Baco Nov. 30, 1926.-. 71,608,875

F. J. BACON ET AL RESONANCE AND AMPLIFYING CHAMBER FOR BANJOS FiledApril 18, 1924 s sheets-sheet 2 gmmtou 6 if cl Bacon p pua l.

Nov. '30 1926. 7 1,608,875

F. J. BACON ET AL RESONANCE AND AMPLIFYING CHAMBER FOR BANJOS 5Sheets-Sheet 3 Filed April 18, 1924 Patented Nov. 30, 1926.

UNITED STATES PATENT OFFECE,

FREDERICK J'. BACON, OF NEW LONDON, AND DAVID L. DAY, OF GRO'ION,CQNNECTIC'UT.

RESONANCE AND AMPLIFYING CHAMBER FOR BANJOS.

Application filed April 18, 1824. Serial No. 707,462.

This invention relates to improvements in resonating chambers for banjosand similar stringed instruments andhas as one of its objects to providea resonating chamber which will greatly amplify and improve the tonesproduced by playing of the instrument, the invention contemplating theprovision of an amplifying chamber so constructed that the sound waveswill be greatly amplilied before they are delivered from the instrument.

Another object of the invention is to provide a resonating chamber whichmay be applied to the rim of any ordinary banjo and readily secured inplace, and which chamber will greatly enhance the tonal qualities of theinstrument.

Another object of the invention is to pro vide a. resonating oramplifying chamber for 2:) banjos so constructed as to provide againstany mufiling of the tones and designed to deliver the tones or soundwaves in a direction forwardly away from the instrument.

Another object of the invention is to provide a Simple and inexpensivemeans associated with the resonance or amplifying chamber and adaptingthe chamber to be applied to the rim of any ordinary banjo with outany'alteration in the construction of the rim or any mutilation of anypart thereof.

Another object of the invention is to so construct the attaching meansthat the amplifying chamber may be readily and quickly applied andequally as readily and quickly removed, so that when employed in therendition of concerts, the amplifying chamber may be attached ordetached in accordance with the nature of the selection to be played.

In the accompanying drawings:

to Figure 1 is perspective view of resonance or amplifying chamberembodying the present invention applied to the rim of a banjo,

Figure 2 is a detail vertical transverse sectional view takensubstantially on the line 2-2 of Figure 1, looking in the directionindicated by the arrows,

Figure 3 is a view in side elevation illustrating a portion of theinstrument and the resonance chamber applied thereto and the meansemployed for holding the said chamber to the rim of the instrument,

Figure 4t is a plan view of one member of the holding or attachingmeans,

55' Figure 5 is a horizontal sectional View taken substantially on theline 55 of F igure 2,

Figure 6 is a view similar to Figure 3, illustrating a slightmodification of the in vention as regards the attaching and holdingmeans. I

In the drawings, the numeral 1 indicates in general a banjo which may beof ordinary or any special construction, the instrument embodying, asusual, a neck 2 extending from the usual rim 3 having the membraneoushead 4; tensioned by the usual tensioning devices embodying each a shank5, a hooked end 6 engageable over the rim 7 which engages in turn, theperiphery of the membraneous head f, the fixed bearing 8 through whichthe stem extends and which bearing is mounted upon the outer side of therim, and the usual nut 9 which is threaded adjust-ably onto the lowerend of the stem 7 and which ordinarily bears against the under side ofthe said bearing 8. These parts are all of the usual construction and donot in themselves enter into the present invention except in therelationship which they bear to the resonance or amplifying chamber ofthe present invention.

The rim 3 and head f of the instrumentconstitute, as usual, a resonancechamber, and the present invention contemplates disposing against theopen back of the rim, an alnplifyingchamber which will increase theresonance of and amplify the tone before delivery from the instrument,thus improving not only the quality but also the volume of the tone. Thesaid amplifying chamber is indicated in general by the numeral 10 andthe same is spun from sheet metal. The said chamber comprises asubstantially fiat, annular top wall indicated by the numeral 11, whichwall is provided at its inner periphery with a depending annular flange12 which is relatively shallow and which is of a diameter substantiallyequal to the external diameter of the rim 3 of the instrument. From thelower edge of the flange 12, an annular partition wall 13 projectsinwardly a suitable distance and defines an opening 14 located centrallyof the said. wall. Viewed in another light, the resonancechamberincludes a top wall which is provided centrally with an opening andwhich, between its inner and outer peripheries, is stepped downwardly soas to accommodate the open side of the rim 3 of the instrument 110 inconnection with which the amplifyingi chamber is to be employed. The topwall 11 at its outer periphery is provided with a downwardly extendingannular flange which constitutes the circumscribing wall 15 of the saidchamber, and this wall is of somewhat greater depth than the flange 12,as clearly shown in Figure 2 of the drawings. The numeral 16 indicates aresonant back which may be of any resonant material such as wood, andthis back is of circular form and preferably bulged as indicated by thenumeral 17, the back being provided with a peripheral rabbet 18 whichreceives the lowor edge portion of the wall 15, screws 19 being securedto said lower edge portion of said wall and into the periphery of thesaid back 16.

As heretofore stated, the open side or back of the rim 3 is adapted tobe more or less snugly received within the circumference of the flange12, as shown in Figure'2 of the drawings, and against the adjacentportion of the partition wall 13., the resonance chamber of theinstrument and the amplifying chamber of the present invention beingplaced in communication with each other by way of the opening 14 whichis, as'stated, defined by the inner periphery of the partition wall 13.By reference to Figure 5 of the drawings, in particular, it will beobserved that the top wall 11 of the amplifying chamber of the inventionsurrounds the rim 3 of the instrument and is formed at equally spacedintervals with openings 20'which are of relatively large diameter;openings 21 which are of smaller diameter; and, openings 22 which, in amanner to be presently explained, accommodate elements of the attachingdevices for holding the amplifying chamber to the, instrument. Theopenings 20 and 21 are alternately arranged as illustrated in thedrawings, and by reference to Figures 1 and 5, it will be observed thatthe openings 20 are located immediately below the tensioning nuts 9.

In that form of the invention shown in Figures 1 to t inclusive, theattaching means for holding the resonance and amplifying chamber to therim of the instrument is indicated in general by the numeral 23 and thesame comprises, in part, a bridge in the nature of a flat arcuate plate24; disposed with its concave edge presented toward the outer side ofthe rim 8 and having its end portions formed with slots 25, the saidplate being formed intermediate its ends and in its convex edge with anotch 26. In mounting the plate in place, the threaded lower endportions of an adjacent pair of the clamps 5 of the head tensioningdevices are fitted through the slots 25, and the nuts 9 of'the'saiddevices then applied to their respective stems and suitably tightened.In this manner, the bridge plate 24 is secured 11 place in positionextending between two adjacent ones of the head tensioning devices andis, therefore, rigidly secured with relation to the rim 3 of theinstrument. The numeral 27 indicates a bolt which is fitted through arespective one of the openings 22 in the top wall 11 of the resonanceand amplifying chamber and which has a headed end 28 located within thesaid chamber, a spring 29 being arranged upon the said bolt within thechamber and bearing at one end the head28 and at its other or upper endagainst the under side of the said wall 11. The upper endof the bolt isthreaded as indicated by the nruneral 30 and extends upwardly throughthe notch 26 in the bridge plate 24L, and a thumb nut 31 is adjustablvfitted-on said threaded end of the bolt and may be adjusted to bear uponthe upper side of the bridge plate and through its adjustment draw thebolt 2'! in an upward direction, hus tensioning the spring 29 andcausing the partition wall 18 of the amplifying chamber to bind firmlyagainst the rear edge of the rim 3, this arrangement of the parts beingmost clearly shown in Figures 2 and 3 of the drawings. The openings 22are preferably located at diametrically opposite sides of the amplifyingchamber 10 on a diametri'c line substantially at right angles to theneckof' the instrument, and while only two of the attaching'and holdingdevices are illustrated as employed in connection with the amplifyingchamber embodying the invention, it will be understood that a greaternumb'er may be employed if found desirable or expedient.

In that form of the invention shown in Figure 6 of the drawings, theattaching and holdingnneansembodies a bridge plate 32 corresponding tothe bridge plate 24;, and fitted through an opening 33 in the said plateintermediate its ends, is an adjusting screw 34: having a slotted head35 adapting it for the application thereto of a screw driver, thethreaded shank of the screw being fitted through an opening 36 in thetop wall 11 of the resonance and amplifying chamber and threaded throughan openii 37 formed in a disc or plate 88 welded or otherwise secured tothe under side of the said wall 11 and of a thickness to have a numberof threads formed in the wall of it; said opening 87. In thisconstruction it is only necessary to apply a screw-driver to the head ofthe screw and adjust the screw so as to draw the resonance andamplifying chamber to the rear edge of the rim of the instrument.

From the foregoing description of the invention it will be evidentthatthe sound waves developed in the resonance box of the'instrument willenter the resonance and amplifying chamber embodying the invention, byway of the opening 14L defined by the annular partition wall 13, and dueto the greater diameter of this chamber as compared to the rim of theinstrument, the resonant nature of its back 16 and its double componentwalls, and due to the firm contact of the rear edge of the rim 3 againstthe metallic partition wall 13 of the said chamber, the sound waves willbe reverberated, the quality of the tone improved, and the volumeincreased, before the sound waves finally are delivered from the saidchamber through the openings 20 and 21 in the wall 11 thereof. Inasmuchas in the playing of the instrument the said wall 11 will be presentedin a forward direction from the player, the sound waves will bedelivered in a corresponding direction and will, therefore, not bemuffled by the clothing of the musician and will carry to a greaterdistance than would be the case if the resonance chamber were notemployed.

It will furthermore be evident that the resonance and amplifying chamberembodying the invention may be readily and quickly applied to andremoved from any ordinary banjo, the rim of which is of a diameterexteriorly to fit within the stepped top wall of the said chamber.

Having thus described the invention, what we claim is:

1. A resonant amplifying chamber for banjos having a continuous annularportion constituting a seat for the edge of the wall of the resonancebox of the banjo and spaced inwardly from its outer periphery and of adiameter to receive the. said resonance box, and attaching means carriedby the chamber, the said chamber being provided in one of its wallsoutwardly beyond the seating portion with sound wave exit openings.

2. A resonant amplifying chamber for banjos having oppositely arrangedresonant walls and a circumferential connecting wall, one of said firstmentioned walls having a continuous annular seat for the rear edge ofthe wall of the resonance box of a banjo and having an opening locatedwithin the circumference of the said seat.

3. A resonant amplifying chamber for banjos having oppositely arrangedresonant walls and a circumferential connecting wall, one of said firstmentioned walls having a continuous seat for the rear edge of the wallof the resonance box of a banjo and having an opening located within thecircumference of the said seat, said wall being provided, outwardly ofthe seat, with sound wave exit openings.

i. A resonant amplifying chamber for banjos comprising an annular wallhaving a portion between its inner and outer peripheries constituting acontinuous annular seat for the open back of the resonance box of thebanjo, acircumferential connecting wall extending about the outerperiphery of the first mentioned wall, and a resonant back disposedwithin the circumference of said circumferential wall, the firstmentioned wall being provided with sound wave exit openings between itsseating portion and its outer periphery.

5. A resonant amplifying chamber for banjos comprising a plane annularwall defining an opening, the inner peripheral portion of said wallbeing offset to provide a depressed seat for the edge of the wall of theresonance box of the banjo, the said wall being provided outwardlybeyond the seating portion with sound wave exit open- I ings, acircumferential wall surrounding the outer periphery of the firstmentioned wall, and a resonant back disposed within the circumference ofthe said circumferential wall.

6. The combination with a banjo including the usual resonance box, headand tensioning devices for the head, of an amplifying chamber having aplane annular wall provided at its inner periphery with an annularflange extending inwardly from the plane of said wall, said flange beingprovided with an inwardly extending resonant partition wall having acentral opening located within the bounds of the wall of the resonancebox, the edge of the wall of the resonance box seating against thepartition wall and within the circumference of the said flange, acircumferential wall extending about the outer periphery of the firstmentioned wall, a resonant back supported within the circumference ofthe said circumferential wall, the first mentioned wall having soundwave exit openings, and means extending between the said first mentionedwall and certain of the said tension ing devices for holding the saidchamber to the resonance box.

In testimony whereof we afiix our signatures.

FREDERICK J. BACON. '[L.s.] DAVID L. DAY. [L.S.]

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